1. Field of the Invention
The invention relates to a gearbox having a first clutch-hub comprising gear-teeth and a coaxial hollow wheel, also with gear-teeth, connected to, but non-rotatable upon, a second clutch-hub, a planetary gear of which the ring-gear is in partial engagement with the said gear-teeth, and a transmission-shaft mounted upon the clutch-hub and arranged between the latter and the said hollow wheel, the said transmission-shaft being adjustable, by means of an adjusting device, in such a manner that the clutch-hub and the hollow wheel rotate selectively, either at rotational speeds between which there is a predetermined difference, or in synchronism, the radially inner clutch-hub being adapted to be secured to the said transmission-shaft for the purpose of synchronous rotation.
2. Description of the Prior Art
German Utility Model No. 1 948 236 describes a gearbox of the type mentioned above in which the clutch-hubs, the drive-shaft and driven shaft are arranged coaxially with each other. Located between the said shafts is a transmission-shaft with an intermediate member having a cutout which partially exposed a pinion connected to the radially inwardly located drive-shaft. The transmission-shaft also comprises a cylindrical, eccentrically arranged section for the toothed ring of a planetary gear. The production of such transmission-shaft is relatively costly. Furthermore, the eccentric section of the transmission-shaft, together with the planetary gear, produce a not negligeable amount of imbalance, leading to comparatively large bearing forces and, possibly, to critical vibration. Moreover, such a gearbox has relatively little elasticity and impacts are therefore transferred practically undamped from one clutch-hub to the other. Because of the imbalance, the known gearbox is not practical for higher rotational speeds.
German Pat. No. 27 42 442 describes a resilient clutch having two central wheels of the same type, with rows of teeth arranged side by side and a planetary gear. The teeth of the planetary gear project into the substantially wedge-shaped virtual tooth-gaps between the central wheels, the profiles of the planetary-gear teeth being in direct engagement with those of the central wheels and being pressed into the gaps between the teeth by radial spring-action. An elastic shaft-coupling of this kind can produce only a direct, synchronous torque-transfer which, in many applications, is a major disadvantage. In this connection, mention may be made of boiler-feed pumps in power-stations which, for safety reasons, must be designed for an approximate 5% overload. By means of chokes in the feed-water valve, or by increasing the slip in a hydraulic transmission-coupling, it has so far been customary to return to the nominal point which involves a considerable loss of power. Since, in the case of turbines, power varies as the cube of the r.p.m., a 5% change in r.p.m. in a centrifugal pump varies the output from the driving machine by 15.7%. The investment required to increase the output of the driving machine is not negligeable. Increased power costs for the driving machine must also be taken into account. It has not been possible to solve these problems with existing shaft-coupling and/or gearboxes.
German Pat. No. 26 17 951 describes a planetary transmission based upon a working mechanism comparable with the above-mentioned elastic coupling. In the case of the planetary transmission, however, the central wheels have different numbers of teeth and the teeth of the resilient planetary gear are forced, by a drive-element, more or less deeply into the gaps between the teeth. A torque-transfer at synchronized rotational speed cannot be obtained with a planetary transmission of this kind.
Finally, German Pat. No. 29 44 123 describes a voltage-surge shaft transmission comprising a drive-motor and a sealed housing. Secured to the housing is a deformable voltage-wheel with which is associated a ring-wheel. A second ring-wheel is secured to an adjusting element. In order to counteract undue deformation, at least one additional support-means, acting in the radial direction, is provided on the driving side of the voltage wheel. The known voltage shaft transmission is to comprise hermetic sealing and to meet extreme safety requirements. Torque-transfer at synchronized rotational speed is not possible, so that the above-mentioned poor efficiency applies here also.